Crankcase made of light metal for an internal combustion engine

ABSTRACT

The description relates to a crankcase made of light metal for an internal combustion engine with a parting plane ( 4 ) running through the crankshaft axis between a case upper part and a case bottom part, whose bearing walls ( 2 ), which connect the case outer walls ( 1 ), are provided with inserts ( 3 ) made of an iron material, in which the bearing shells of the crankshaft bearing and the bearing bolts ( 7 ) provided on both sides of the bearing shells are borne. To achieve favorable construction features it is suggested that the bearing walls ( 2 ) forming a continuous light metal bridge between the case outer walls ( 1 ) accommodate the inserts ( 3 ) that are lower than the bearing walls ( 2 ) in recesses ( 8 ) starting from the parting plane ( 4 ) and are provided, in the area of the bearing bolts ( 7 ), with through holes ( 9 ) for the bolt heads ( 10 ).

CROSS REFERENCE TO RELATED APPLICATIONS

Applicants claim priority under 35 U.S.C. §119 of AUSTRIAN ApplicationNo. A949198 filed JUN. 3, 1998. Applicants also claim priority under 35U.S.C. §120 of PCT/AT99/00136 filed on MAY 31, 1999. The internationalapplication under PCT article 21 (2) was not published in English.

FIELD OF THE INVENTION

The invention relates to a crankcase made of light metal for an internalcombustion engine with a parting plane running through the crankshaftaxis between a case upper part and a case bottom part, whose bearingwalls, which connect the outer case walls, are provided with insertsmade of an iron material, in which the bearing shells of the crankshaftbearing and the bearing bolts provided on both sides of the bearingshells are borne.

DESCRIPTION OF THE PRIOR ART

To achieve, in case of crankcases made of light metal, a favorable loadtransmission from the cylinder head to the crankshaft and to obtain, inthis context, a rigid support of the crankshaft bearings, it is known(U.S. Pat. No. 5,203,854) to bear the crankshaft bearings by means ofthe bearing bolts in gray cast iron inserts of the bottom part of thecrankcase. These inserts of gray cast iron that are sealed between thecase outer walls and that form the core of the bearing walls, aredimensioned as a function of the load applied to the crankshaft bearingand, due to this dimensioning, determine the height of the crankcasebottom part. As the vibration behavior and thus the impact soundbehavior of the crankcase depends on its flexural strength, the elasticmodulus and the moment of inertia are decisive with respect to theimpact sound behavior. The elastic modulus of light metals, as they areused for crankcases, is approximately only half the elastic modulus ofgray cast iron, so that, with respect to the impact sound behavior,crankcases of light metal are inferior to those of gray cast iron,unless the moment of inertia is increased by means of suitableconstructive measures, thus ensuring a sufficient flexural strength. Tothis end the crankcase may be stiffened via the connected lowercrankcase, which, in this case, must be designed rather complex. But inspite of the use of such complex lower crankcases the impact soundbehavior of the known crankcases made of light metal remainsunsatisfactory.

SUMMARY OF THE INVENTION

It is therefore the objective of the invention to improve a crankcasemade of light metal of the above mentioned kind in such a way that asatisfactory impact sound behavior is achieved without a complex designof the lower crankcase, without having to expect any adverse effects onthe crankshaft bearing.

The objective of the invention is achieved in that the bearing wallsforming a continuous light metal bridge between the case outer wallsaccommodate the inserts, which are lower than the bearing walls, inrecesses starting from the parting plane, and are provided, in the areaof the bearing bolts, with through holes for the bolt heads.

Via these measures it is for one thing ensured that the inserts made ofan iron material can be dimensioned solely as a function of the loadapplied to the crankshaft bearings and/or of the dimension of thebearing bolts, without having to accept a limitation of the height ofthe case bottom part due to these inserts. As the overall height of thecase bottom part may now be considerably higher compared to the inserts,the intended higher flexural strength of the crankcase is achieved, anda complex lower crankcase can be avoided. Thus it is achieved that thestructural parts made of an iron material, which take up the load of thecrankshaft bearing, and the light metal parts can be dimensionedindependent of each other, which leads also to a favorable constructionwith respect to both sound impact behavior and load transmission,because a sufficient height of the case bottom part, as it is necessaryfor the desired flexural strength can be ensured, independent of theheight of the inserts.

If the height of the bearing walls is at least half the internaldistance of the case outer walls, particularly favorable constructionfeatures are achieved, not only providing a high flexural strength ofthe case bottom part, but also permitting the use of a conventionalsupporting lower crankcase in the form of a simple pan cover, as in thiscase a considerable part of the lower crankcase as usual otherwise isformed by the case bottom part proper.

Moreover, as the inserts made of an iron material are embedded inrecesses, starting from the parting plane, in the light metal bridges ofthe bearing walls running through between the case outer walls, the useof a sintered material is supported, which implies favorablemanufacturing conditions, in fact without any loss of strength.

BRIEF DESCRIPTION OF THE DRAWING

The drawing depicts an example of the subject matter of the invention.

FIG. 1 shows a detail of the case bottom part of a crankcase accordingto the invention in a schematic diagram,

FIG. 2 represents the case bottom part in a cross section through abearing wall, and

FIG. 3 depicts a detail of the case bottom part in the area of a bearingwall in a bottom view.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The depicted case bottom part of a crankcase made of light metalaccording to the invention is provided with case outer walls 1 runninglongitudinally in the conventional way, as well as bearing walls 2connecting these case outer walls 1 and directed transverse thereto,which are equipped with inserts 3 made of an iron material, preferablysintered metal. These inserts 3 form accommodations 5, starting from theparting plane 4 to the case upper part and shaped semicircular, for thebearing shells of the crankshaft bearings. On both sides of theseaccommodations 5 there are bores 6 for the bearing bolts 7 provided inthe inserts 3, via which bores 7 the load transmission from the cylinderto the inserts 3 is effected.

Contrary to conventional case bottom parts of this kind the inserts 3made of an iron material cover only part of the height of the bearingwalls 2, so that the bearing walls 2 form a continuous light metalbridge between the case outer walls 1. The inserts 3 are embedded intorecesses 8 of the bearing walls 2 starting from the parting plane 4,which are provided in the bottom area of the recesses 8 with throughholes 9 for the bolt heads 10 of the bearing bolts 7. Therefore, thebearing bolts 7 can be pushed via the through holes 9 into the bearingbores 6 of the inserts 3 and bolted with the case upper part.Consequently, for dimensioning the bearing bolt 7, the different thermalexpansion behavior of the inserts 3 and the light metal bridges of thebearing walls 2 accommodating the inserts 3 need not be considered,although the height of the bearing walls 2 considerably exceeds that ofthe bearing inserts 3 at least in the area of the inserts 3. This meansthat the inserts 3 can be dimensioned first of all according to the loadrequirements for taking up the bearing forces, without considering therequired flexural strength of the case bottom part, so that the share ofweight of the inserts 3 can be favorably limited. The high flexuralstrength of the case bottom part, required with respect to impact soundbehavior, must be ensured via an increased moment of inertia due to thelower elastic modulus compared to that of light metal, which demandsabove all a higher overall height of the case bottom part. Due to theheight of the bearing walls 2 independent of the height of the inserts3, this requirement is easiliy met. Thus it is possible to accommodatethe lower crank space within the case bottom part, as this is outlinedby the dash-dotted circular line 11 in FIG. 2. Thus a conventional lowercrankcase for additionally stiffening the crankcase may be omitted andreplaced by a simple cover for the case bottom part.

By means of the described measures it is comparatively simple to obtaina favorable impact sound behavior of a crankcase made of light metalwithout having to accept drawbacks in the field of load transmission viathe crankshaft bearings or with respect to weight conditions.

What is claimed is:
 1. A light metal crankcase for an internalcombustion engine, which comprises an upper crankcase part and a lowercrankcase part, with a parting plane running through a crankcase axisbetween the upper and lower crankcase parts, the lower crankcase partcomprising two opposite outer walls, light metal bearing wallsconnecting the outer walls and forming continuous light metal bridgesbetween the two opposite outer walls, the light metal bearing wallsdefining recesses starting at the parting plane, inserts of ironmaterial received in the recesses, the inserts being shorter than thebearing walls and defining bearing shells for a crankshaft, and bearingbolts having heads mounted in bores in the inserts at each side of theinserts, the bearing walls having through holes aligned with the boresfor receiving the heads.
 2. The light metal crankcase of claim 1,wherein the bearing walls have a height which is at least half theinternal distance of the two opposite outer walls.
 3. The light metalcrankcase of claim 1, wherein the inserts are of a sintered ironmaterial.